Why did GNU choose UNIX?

Or rather, why did rms et al dislike UNIX? It seems to come up a lot that they basically settled for a UNIX clone since it was widespread. They certainly didn't care for the philosophy.

>>1
He played with the idea of a free OS based on the lisp-machines but deprecated the idea.

In order to run safer LISP code on them you had to had a microcode for the machine or the type-inference wouldn't work. Also the performance of IBM machines on LISP was getting better than in lisp-machines.

He admits that never played with unix before the GNU project, but thinks that overall the solution was correct

weird how old rms was more pragmatic than now